This invention relates generally to manufacturing antennas repeatably in high volume for a variety of applications and integration environments. More particularly, the present invention relates to a method of mechanically tuning antennas for low-cost, volume production.
There are various realizations of internal antennas for portable devices, but a select few embodiments are most common due to the need for low cost and reproducible manufacturing approaches. Internal antennas are those contained wholly within a radio product, as distinct from external antennas such as whip antennas or antennas that may be extended from an internal stowed position to an active position. These antennas are typically small, but there is no well defined upper limit to the size and form factor of such antennas.
Antennas are often fabricated using stamped metal draped over plastic, patterned fiberglass (FR4) Printed Circuit Board (PCB) material, or metallized and patterned plastic. FIG. 1 shows an example of a prior art antenna assembly 100 in which a metal antenna is supported on a plastic support structure. The antenna assembly 100 includes a sheet metal antenna and a plastic support mounted on a ground plane. Construction of the antenna assembly 100 requires bending the sheet metal into the desired antenna shape, and draping the antenna sheet metal over the plastic stand-off or support. The metal is either stamped out of a separate piece of metal or may be plated directly on plastic.
A second example of prior art antenna construction uses insert molded plastic. One material which may be used is Liquid Crystal Polymer (LCP) for the molded plastic and plated copper for the insert metal. Other materials may be substituted for the LCP and copper as required by particular design and product requirements. The LCP can withstand high temperatures, and is compatible with standard Surface Mount Technologies (SMT) for assembly. Micro-injection molding the antenna allows tight mechanical tolerance control of all dimensions of the antenna.
Manufacturers of wireless devices such as radiotelephone handsets, personal digital assistants (PDA's) and laptop computers are constantly pressured to reduce the size and cost of their products. Existing antenna solutions often shift frequency response when they are integrated into products. More seriously, the amount of frequency shift is different for each application, and is often different for very similar applications. For instance, an original equipment manufacturer (OEM) which produces laptop computers may have many different laptop models, or platforms. Current antennas would “de-tune” by a different amount for each platform, or for different mounting locations within one given platform. This forces the OEM to carry multiple part numbers of antennas for each integration into these multiple model numbers. This drives product cost upwards due to increased inventory requirements, lower economies of scale, and increased complexity and logistics associated with multiple antenna solutions.
Often, there are extensive up-front tooling costs to manufacture antennas, especially if the antennas are molded out of plastic. This tooling cost is a significant portion of the total cost of the antenna. If slightly different antennas are needed for each and every application, the antenna's unit cost would be prohibitive. Hence, there is a real need for either an antenna that is less sensitive to installation effects, or an antenna that can be easily modified during production so that tooling costs are not affected.